1. Field of the Invention
This invention relates generally to interventional medical devices, and more particularly concerns an optical fiber composite shaft having variable stiffness for enhanced performance of the composite shaft when used with or without a guide catheter, or as a stand-alone flow directed device for use in the vascular system as part of an imaging system, a therapeutic system or for delivery of medical devices.
2. Description of Related Art
Conventional minimally invasive catheter based therapies typically require guide wires that are one to two meters long extending through a longitudinal lumen in the catheter, and that are torqueable and pushable at the proximal end, yet soft and flexible at the distal end. Many such guidewires are made of stainless steel or the like, and are ground to tapers which provide the desired bending properties along the guidewire. Recently, numerous minimally invasive sensing and actuation procedures have been developed which benefit from the unique qualities of an optical fiber to deliver optical light or power to the distal tip of the optical fiber. For example, optical fiber based technology can be used for imaging, treatments such as xe2x80x9cthrombolyzingxe2x80x9d blood or cutting tissue by use of high energy light delivered through the end of the optical fibers, and for the delivery of therapeutic agents, such as timed release agents or embolics. However, conventional optical fiber technology has not been easily adaptable to such applications, particularly when the optical fiber must also act as a guidewire, either within a catheter or as a stand-alone device, since optical fibers, when used alone, are not very torqueable, pushable or resilient when compared to guide wires made from a variety of other, more rigid, materials. Also, small diameter optical fibers are quite xe2x80x9cfloppyxe2x80x9d, while larger diameter fibers can be too stiff to maneuver through sharp bends, and the use of optical fibers as guidewires or pushers within catheters can thus be difficult and quite technique sensitive.
An abdominoscope is known that includes a tubular sheath having a series of strips separated by longitudinal slots, and an elongate, steerable, flexible medical implement is also known that has a tubular body with a controllable steering region formed from flexible steering ribbons made of flexible materials, such as Nitinol, spring steel, nylon, or other plastic material. In addition, a steerable medical probe is also known that has a torque tube with spaced apart slots to impart additional flexibility to the torque tube, with a thin-walled connecting portion serving as a rib or backbone. However, there remains a need for a way of creating variable stiffness along an optical fiber shaft, without a decrease in the torquability, pushability and resistance to fracture of the optical fiber shaft.
It would also be desirable to provide an optical fiber shaft with variable stiffness to allow optical fibers to be more pushable at the proximal end and more trackable at the distal end, and to make the use of optical fibers in catheter-based therapies more straight forward and less technique sensitive. The present invention addresses these and numerous other needs.
Briefly, and in general terms, the present invention provides for a variable stiffness optical fiber shaft formed from an optical fiber and a reinforcing tube over at least a portion of the optical fiber, with apertures being formed around the surface of the reinforcing tube and extending in a direction between the proximal and distal ends of the optical fiber, to provide variable stiffness to the optical fiber shaft. By use of the invention, a variable stiffness shaft can be made which is more pushable at the proximal end and more trackable at the distal end, with the capability to provide a wide range of predictable variations in stiffness and other structural parameters over the length of the shaft. A variable stiffness optical fiber shaft constructed according to the invention can be used in conjunction with a guide catheter or as a flow directed, stand alone catheter.
By using the construction according to the invention, coating or heat shrinking a heat shrinkable material on the outside diameter of the optical fiber will improve tracking of the device, and a taper can also be ground onto the optical fiber shaft to yield a shaft with a stiffer, more manageable, proximal end and a softer, more maneuverable, distal tip. The variable stiffness optical fiber shaft advantageously can also thus be constructed from a minimum number of components, with the apertures in the reinforcing tube eliminating the need for a braid or transitional sections from the stiffer proximal zone to the softer distal zone.
The invention accordingly provides in a presently preferred embodiment for a variable stiffness optical fiber shaft for use in vascular interventional therapy, such as for use within a tortuous, small diameter vessel such as those found in the vasculature of the brain. The variable stiffness optical fiber shaft comprises an optical fiber having a proximal end and a distal end, a reinforcing tube attached to the optical fiber, with the optical fiber extending through the reinforcing tube, and the reinforcing tube having a surface defining a plurality of apertures extending in a direction between said proximal and distal ends of said optical fiber, and at least one coaxial outer layer of a polymer, metal, or both provided over at least a portion of the reinforcing tube and the optical fiber, for providing desired variations in stiffness along at least a portion of the length of the shaft. The reinforcing tube is preferably a metal tube, such as a hypo tube, and can be formed of stainless steel or an alloy of nickel and titanium, for example.
In one presently preferred embodiment, the apertures can be formed as longitudinal, axial slits, slots, channels, or grooves in the surface of the reinforcing tube, and in an alternate preferred embodiment, the apertures can be formed as helical or radial slits, slots, channels, or grooves in the surface of the reinforcing tube, providing variable stiffness to the optical fiber shaft. The outer surface of the reinforcing tube can also be formed to be tapered at the point where the apertures are formed in the reinforcing tube, particularly at a distal portion of the optical fiber, to provide an optical fiber shaft that is torqueable and pushable at the proximal end, yet soft and flexible at the distal end. Alternatively, the apertures can be formed transversely in the surface of the reinforcing tube in an area where such a configuration will produce desired results.
The one or more coaxial layers can be formed of heat shrink polymeric material, such as polyethylene, polytetrafluoroethylene (PTFE) polyethylene terephthalate (PET), polyetherethylketone (PEEK), polyphenylenesulfide (PPS), or any of a variety of other polymers which can be fabricated into a structure and necked or shrunk over a shaft, or can be formed of metal. While the invention can effectively use tubes which are placed over the exterior of the optical fiber shaft and then heat shrunk or bonded by adhesive to the fiber, it is also contemplated that the shaft can be reinforced by other longitudinally extending additional structures with varying cross sections for certain specific applications.
The heat shrink tubing is placed on the fiber, and then heat can be applied to the heat shrink tubing, resulting in shrinkage of the heat shrink tubing to encapsulate the fiber. The structure formed by the apertures in the surface of the reinforcing tube, in combination with the distal taper of the reinforcing tube and outer coaxial sheath, allows the proximal part of the composite shaft to be relatively stiff, and the distal tip to be flexible and soft. A variety of other techniques can be used within the scope of the invention to accomplish the variable stiffness of the optical fiber shaft.
Those skilled in the art will also recognize that, while the invention has been described in the context of optical fibers, other, equally non-structural fibers used for therapeutic or measurement purposes may also benefit from the invention.
These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings, which illustrate by way of example the features of the invention.